Introduction
The response to stress is genetically predetermined, since it has been honed by many years of evolution and ancestral environmental exposures. To be able to respond to the environment in a manner similar to their parental cells, each cell has to undergo faithful DNA replication [1]. In addition, all epigenetic marks need to be reproduced. In a stable environment, daughter cells look similar to parental cells in their genetic and epigenetic makeups and often in the set of various metabolites, with variations attributed typically to the developmental stage or tissue specificity (Box 1). Fluctuations from a stable environment trigger different responses from plants, occurring on biochemical, molecular, and cellular levels, and including changes in primary and secondary metabolites and epigenetic marks, allowing plants to survive stress [2,3]. When stress is no longer present, most of these changes disappear [3], but some are maintained [4], allowing daughter cells to receive the information about the response to stress, allowing plants to acquire partial protection (Box 1). This somatic stress memory could include various metabolites, as well as changes in DNA methylation or modifications of histone tails [4]. This was recently demonstrated in rice in response to salt—biochemical and epigenetic changes were noted, correlating with stress tolerance [4]. Similarly, the metanalysis of reports on the memory of stress applied prior and during seed germination showed that the memory was based on the changes at the level of chromatin reorganization, alternative transcript splicing, metabolite accumulation, and autophagy [5]. This memory allows the plant to perform better when stress returns. The most well-known examples of such a response to stress are acclimation and adaptation [6].
Box 1. Changes in response to environment.
Adaptation—the process of permanent changes in plant metabolism and phenotype in response to a changed environment, observed in an entire population of plants.
Acclimation—the process of adjustment to changes in the environment, allowing individual plants to maintain fitness and continue/complete their developmental process. Typically, this is a short-term somatic process. Some scientists consider the inheritance of this response as transgenerational acclimation, also referred to as phenotypic plasticity. The changes are lost when the stimulus is not maintained.
Normal environmental conditions—fluctuations in abiotic growth conditions, including temperature, water, light regimes, and biotic interactions to which a specific plant species is adapted. Certain conditions may be the norm for one species or population, but not for another.
Priming—exposure to a mild stress that results in a higher tolerance to a more severe stress of the same or similar nature. Priming effect, sometime referred to as hardening, may be heritable in nature, representing an intergenerational memory of stress.
Latent period—time between the stress exposure and accumulation of molecular and physiological changes required for stress tolerance.
Somatic stress memory—the features of acclimation or tolerance (or intolerance), be it phenotypic or epigenetic in nature, to subsequent stress exposures.
In this review, the somatic stress response and priming will be described in more detail, and various mechanisms of epigenetic response to stress, including chromatin decondensation, the role of chromatin modifiers, histone modifications, changes in DNA methylation, the activity of non-coding RNAs, and RNA methylation, will be presented.
References
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Journal: Plants Author: Kovalchuk
Introduction The response to stress is genetically predetermined, since it has been honed by many years of evolution and ancestral environmental exposures. To be able to respond to the environment in a manner similar to their parental cells, each cell has to undergo faithful DNA replication [1]. In addition, all epigenetic marks need to be reproduced. In a stable environment, daughter cells look similar to parental cells in their genetic and epigenetic makeups and often in the set of various metabolites, with variations attributed typically to the developmental stage or tissue specificity (Box 1). Fluctuations from a stable environment trigger different responses from plants, occurring on biochemical, molecular, and cellular levels, and including changes in primary and secondary metabolites and epigenetic marks, allowing plants to survive stress [2,3]. When stress is no longer present, most of these changes disappear [3], but some are maintained [4], allowing daughter cells to receive the information about the response to stress, allowing plants to acquire partial protection (Box 1). This somatic stress memory could include various metabolites, as well as changes in DNA methylation or modifications of histone tails [4]. This was recently demonstrated in rice in response to salt—biochemical and epigenetic changes were noted, correlating with stress tolerance [4]. Similarly, the metanalysis of reports on the memory of stress applied prior and during seed germination showed that the memory was based on the changes at the level of chromatin reorganization, alternative transcript splicing, metabolite accumulation, and autophagy [5]. This memory allows the plant to perform better when stress returns. The most well-known examples of such a response to stress are acclimation and adaptation [6]. Box 1. Changes in response to environment. Adaptation—the process of permanent changes in plant metabolism and phenotype in response to a changed environment, observed in an entire population of plants. Acclimation—the process of adjustment to changes in the environment, allowing individual plants to maintain fitness and continue/complete their developmental process. Typically, this is a short-term somatic process. Some scientists consider the inheritance of this response as transgenerational acclimation, also referred to as phenotypic plasticity. The changes are lost when the stimulus is not maintained. Normal environmental conditions—fluctuations in abiotic growth conditions, including temperature, water, light regimes, and biotic interactions to which a specific plant species is adapted. Certain conditions may be the norm for one species or population, but not for another. Priming—exposure to a mild stress that results in a higher tolerance to a more severe stress of the same or similar nature. Priming effect, sometime referred to as hardening, may be heritable in nature, representing an intergenerational memory of stress. Latent period—time between the stress exposure and accumulation of molecular and physiological changes required for stress tolerance. Somatic stress memory—the features of acclimation or tolerance (or intolerance), be it phenotypic or epigenetic in nature, to subsequent stress exposures. In this review, the somatic stress response and priming will be described in more detail, and various mechanisms of epigenetic response to stress, including chromatin decondensation, the role of chromatin modifiers, histone modifications, changes in DNA methylation, the activity of non-coding RNAs, and RNA methylation, will be presented.
References